Docker containers are one of the hottest technologies around at the moment, so much so that CoreOS even built its Linux-based operating system for large server deployments around the concept.

But now CoreOS isn’t happy with the direction Docker is taking. Docker has a “broken security model”, and so it’s decided to build an alternative container runtime called Rocket to compete with it. And so the “container wars” have officially begun.

Late on Monday, CoreOS unveiled the first prototype of Rocket, which it describes as a command-line tool for managing App Container, its container image format, discovery and runtime mechanism.

“We still believe in the original premise of containers that Docker introduced, so we are doing something about it,” wrote CoreOS CEO Alex Polvi in a blog post. “While we are at it, we are cleaning up and fixing a few things that we’d like to see in a production ready container.”

Polvi says he believed Docker’s development has drifted apart from the original concept of standard containers. Now it’s slowly becoming “Docker-as-a-platform”, and that’s not what Polvi had in mind when he first began working with the technology.

“Unfortunately, a simple re-usable component is not how things are playing out,” Polvi explained. “Docker now is building tools for launching cloud servers, systems for clustering, and a wide range of functions: building images, running images, uploading, downloading, and eventually even overlay networking, all compiled into one monolithic binary running primarily as root on your server.”

Like Docker, Rocket is essentially a container engine, only it comes without all of the extras that have been piled onto Docker to make the tech more enterprise-friendly. The current version of Docker adds tools for spinning up cloud servers, networking capabilities and the ability to add clustered systems.

Docker CEO Ben Golub has already responded to CoreOS’s move in a blog post, saying it’s a disappointing development. He added that “only a small number of vendors” shared its opinion about Docker’s direction, and that those who disagreed usually did so for selfish reasons. Nevetheless, as Golub admitted, Docker is an open-source project, and so customers are free to use the software as they like, even if that means creating a ‘rival’ to Docker itself.

“While we disagree with some of the arguments and questionable rhetoric and timing of the Rocket announcement, we hope that we can all continue to be guided by what is best for users and developers,” Golub said.

Rocket and App Container are still a work in progress and so it’ll be a while before we know if it has the potential to disrupt Docker itself. But CoreOS is hoping the open-source community will work with it to develop the new technology. It’s prepared a draft of App Container’s specs here, while the prototype of Rocket can be found here.

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